The injection molding is a method for forming a product identical to a cavity formed in a mold by introducing and filling molten resin into the cavity of the mold of a certain shape and cooling the resin filled in the cavity thus. Recently, along with development of the MEMS technology, different shapes of structures are produced by using the stampers having the micro patterns formed thereon.
Particularly, the injection molding is a general method for mass production of plastic products. Since demands on plastic products of high strength polymer with a long durability increase significantly as the times develop, the injection molding is also being applied to various fields, presently.
Recently, the injection molding is applied, not only to general domestic plastic products, but also even to production of plastic products to be used for a space-air field or a precision optical instrument field, particularly to products which require micro and precise patterns.
That is, the injection molding is used for producing a plastic structure having a micro pattern with a size of a few tens of nanometers to a few tens of micrometers formed on a surface thereof.
In the meantime, in order to provide such a plastic structure having the micro pattern with a size of a few tens of nanometers to a few tens of micrometers, a separate stamper corresponding to the micro pattern is used. In general, the stamper is provided in a shape of plate.
A molded product which can produce an optical effect caused by constructive interference and destructive interference of a light can be manufactured by using the stamper having the micro pattern. For an example, a nano-line width of the micro pattern can be used for a high resolution spectrometer, or a pattern which accelerates scattering of the light can be used for a back light unit of a liquid crystal display device.
Or, by making a photonic band gap effect to take place with a regular arrangement of the micro patterns, the micro pattern can be made to have a feature in which the micro pattern reflects a light of a particular wavelength while transmitting or absorbing lights of other wavelengths.
In general, in order to form a desired micro pattern, the stamper having such a pattern is used. In order to form a prior art micro pattern, the LIGA (Lithographie, Galvanoformung, Abformung in German) process is used.
A process for manufacturing the stamper by using the LIGA process will be described. At first, a substrate is subjected to washing, photoresist coating, and soft baking. Then, the substrate is subjected to exposure and development with a pattern mask of a predetermined shape placed on the substrate. And, a hard baking is performed at a portion having the photoresist removed therefrom, to form the micro pattern of a predetermined shape. After depositing a conductive layer on the pattern formed thus, nickel or copper is plated on the pattern, and a layer of the plating is separated to finish formation of a master stamper.
FIG. 1 illustrates a photograph of a prior art stamper for injection molding.
Since the master stamper manufactured thus has the micro pattern formed thereon, and is used as a mold for producing injection molded products, the master stamper is required to maintain a smooth mirror surface. However, since the prior art master stamper has low hardness of a pattern surface of the nickel or copper, the master stamper has a problem in that, as shown in FIG. 1, a scratch S is formed even by slight contact, and maintenance is difficult.